Developments in biological standardization最新文献

SmithKline Beecham Biologicals produces two vaccines against hepatitis: hepatitis B (Engerix-B) introduced in 1986 and hepatitis A (Havrix) introduced in 1991. Using these two examples, we demonstrate the long and gradual transition process towards an in vitro release test for potency and a significant decrease in the number of animals needed for vaccine release.

Modern physicochemical methods allow biological pharmaceuticals, particularly those arising from recombinant DNA technology, to be characterised with a degree of precision not previously possible. These techniques, which tell us what a material is (rather than what it does) provide an approach complementary to traditional bioassays for the control of biological pharmaceuticals. As we come to understand the mechanisms by which structural variation modulates the various biological activities of a product, structure-based assays will be able to replace biological identity and potency assays, although replacement of safety tests to find trace impurities (such as endotoxin) may be more difficult.

Consideration of alternative methods for animal tests in developing countries is important because good quality laboratory animals and proper animal facilities are not always sufficiently available to perform the currently required quality control tests. In vitro methods have been implemented at the National Institute of Vaccines and Biological Substances (IVAC) in Vietnam. These include serological tests (such as the Toxin Binding Inhibition test and the VERO Cell test) for the estimation of potency of Tetanus and Diphtheria toxoid vaccines and for the evaluation of vaccine field trials. Currently, an inhibition ELISA test to determine anti-rabies activity in equine rabies immunoglobulin preparations is being developed with the long-term goal of its introduction in Vietnam. The results from validation studies are promising and have contributed to decisions made by the National Control Authority to replace imported DPT vaccines in the EPI program with Vietnamese-produced DPT vaccines. This paper summarizes IVAC's experience in introducing alternatives in Vietnam over the last 10 years and reports on the various local validation studies which were performed during this period.

International standards are used to assess the potency of a variety of biological drugs employed in the field of haemostasis and thrombosis. These include therapeutic concentrates for the treatment of inherited coagulation defects, such as haemophilia, thrombolytic drugs such as streptokinase for the treatment of heart attacks, and anticoagulant drugs such as heparin. Some of these standards have existed for over 25 years, and they continue to play a vital role in ensuring consistent potency, and hence safety, of manufactured drugs. The growing complexity of new products, particularly in the area of recombinant technology, represents a continuing challenge for the field of biological standardization.

MDCK cells have been adapted to grow in a serum-free environment using Ultra-MDCK medium (BioWHITTAKER). The growth of adapted U-MDCK cells was maintained for over a year without any reduction in growth rate or modification of cell karyotype; cells were scaled up to spinner culture using several microcarriers. The cells were shown to be a very good host for influenza A and B virus replication in both the presence and absence of trypsin in the infection medium. Trypsin-independent viruses replicated to high titres (10(7)-10(8) TCID50/ml) in U-MDCK cells, after selection through serial passages without trypsin. This virus progeny exhibited uncleaved and antigenically modified haemagglutinin compared with standard viruses grown with trypsin. Finally, large amounts of influenza A and B viruses were produced in U-MDCK cells grown on microcarriers under rod-stirred conditions using selected trypsin-independent variants.

The replacement of embryonated chicken eggs by tissue culture cells for the production of influenza vaccines is likely to take place in the near future. Vaccines have already been produced in Madin Darby Canine Kidney (MDCK) cells (Brands et al, in this issue) and extensively tested in phase III trials in humans (Palache et al, in this issue) and it seems a matter of time before such vaccines will become available. For this reason, the generation of high-growth reassortants of influenza A virus strains in MDCK cells has been examined. Influenza A virus reassortants of the field strains A/Taiwan/1/86, A/Johannesburg/82/96 and A/Shenzhen/227/95 (all H1N1) were generated in serum-free cultured MDCK-SF1 cells by dual infection with A/Hong Kong/2/68 (H3N2), a strain selected for its high-growth phenotype. These reassortant viruses all contained at least the matrix gene of A/Hong Kong/2/68 which apparently correlates with an improvement of the viral yield.

We have found that our MDCK-derived cell line (BV-5F1) is non-tumorigenic in tests conducted in accordance with FDA guidelines, and thus may be suitable for producing live, attenuated or inactivated vaccine. The cell line has been extensively tested for the presence of contaminating microorganisms. No infectious agents of viral or other microbial origin were present. Using the BV-5F1 cell line, we have now designed a process for the large-scale production of influenza virus for the manufacture of a vaccine. The production system involves expansion of cells anchored on a microcarrier using stirred fermenters, followed by virus infection. Viral particles are purified in a way similar to the licensed egg-derived vaccine Fluviral SF and mainly involves ultracentrifugation, ultrafiltration and formaldehyde inactivation. The final product is a split inactivated vaccine. A randomized, double-blind clinical study was made in healthy adults using the new split influenza vaccine derived from viruses grown in cell culture (bivalent formulation). The results of this Phase I study have demonstrated that the split influenza vaccine derived from cell culture is highly immunogenic and safe in adults.

The paper presents an overview of current public policy issues relating to biological standardisation and control, drawing on the extensive background material assembled for two recent international reviews, and previously published work. It identifies a number of factors which are destabilising the current system and promoting a climate for change. These include the squeeze on public sector resources, the growth in volume and complexity of biologicals, developing world needs, concerns about harmonisation and new social and ethical issues. It is argued that this situation presents important opportunities for reviewing the existing boundaries between regulatory scientists, industry, and the public, for international agreement on priorities and for harmonisation and mutual recognition. While considerable progress has already been made on these issues at national, regional and global level, there is a need for fuller international participation and the additional impetus that would come from a higher-profile commitment by governments. Such commitment will also be important for the vital questions of sustaining the scientific base and securing the resource for an effective, truly worldwide programme of standardisation and control. An international approach will also be essential in steering biologicals control through the difficult social and ethical questions of the future. WHO, in collaboration with national authorities, has a key role to play in these developments.

Henry Dale, a Nobel laureate and statesman of science, helped to organize the meetings in 1923 and 1925 to set up international standards for insulin and other biologicals. He made the National Institute for Medical Research one of the two world centres for standards. Some milestones in the work of the London centre are described: (i) the first standards; (ii) vitamins and hormones; (iii) WHO standards for many antibiotics; (iv) the provision of an international working standard for ACTH; (v) the old and new methods of ampouling; (vi) the impact of research and immunoassay on the need for standards; and (vii) the special ECBS sessions for endocrinology and haematology. Dale tells how he had to preserve the first batch of insulin for use as the standard instead of for treatment.